Telephone system



July 4, 1950 o. A. PEArcE EI'AL 2,513,964

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TELEPHONE SYSTEM Filed July 2'7, 1945 19 Sheets-Sheet 19 (sFBo-23) (652 10-23) a 23 a 313 I 9 31 9 321 1a 131 1a 34 6M 19 132 19 41 2o 133 42 INVENTORS OWEN AVIS PEARCE GEORGE THOMAS BAKER I BY% Z:

ATTORNEY Patented July 4, 1950 TELEPHONE SYSTEM Owen Avis Pearce and George Thomas Baker,

Liverpool,

England, assignors to Automatic" Electric Laboratories Inc., Chicago, 111., 'a corporation of Delaware Application July 27, 1945, Serial No. 607,472 In Great Britain August 25, 1944 15 Claims. 1

The present invention relates to telephone systems and has for its general object to provide a readily expandable small automatic telephone exchange board of the private or rural type.

A further object of theinvention is concerned with an improved method for associating calling lines with the numerous special facilities which are oftenrequired on such boards and it is also concerned with improved methods of initiation and control of such facilities. I I

On private automatic exchange boards in particular the general practice is to provide basic selecting equipment for the setting up of conversational connections between subscribers, the design of such equipment differing according to the line capacity and trafiic considerations of the board concerned. Furthermore, where any special facilities are required such as service to other interconnected private automatic exchanges (tie lines), code call and fire alarm services and the like the general procedure has been to incorporate as much as possible of the circuits for these features in the basic circuits of the board. Since both the line capacity and the special services vary from board to board the number of circuit combinations involved is large and this militates against mass production of such boards. I

According to the present invention asmall automatic exchange board is arranged to be built up from one or more identical units each comprising a number of local finder/connector links, tie line service links and other special service links being provided in individual units which can be added to the board at will.

According to a feature of the invention in response to the dialling of a suitable number a special service linkis adapted to associate itself with a calling line by a finding operation, whereupon the local link previously taken into use is released for further use.

According to another feature of the invention a priority subscriber on setting up a call to an engaged line is enabled to cut in on to said line by dialling an additional digit of predetermined value.

According to a further feature of the invention, after a watchmans service link has associated itself with a calling line in response to the dialling of a suitable code number the dialling of an additional digit of predetermined value serves to enable telephone communication to be efiected between the calling party and a central station.

According to a further feature of the invention the finder switches of both local and special service links are served by a common set of 2 allotting switches the banks of which are subdivided in such manner as to give access to the various types of finders required according to the circumstances of the call concerned. The common'allotting' switches also serve to allocate an order of priority to the various different findihg operations in cases where two or more different finding operations are being initiated simultaneously. I

According to a further feature of the invention, after the dialling of the selecting digits necessary to associate a calling line with a called line the dialling o fYa further digit of predetermined value is, if the line is either disengaged or if the callhas not been accepted, adapted to result in the association of a code call link with the called line. I

According to still another feature of the invention a local link is adaptedto respond to' an additional dialled digit-after a line selecting operation has been performed the normal or operated condition of the called subscribers battery feeding relay in the link circuit serving to determine whether or not a special service link shall be brought into operation. I I I The invention willbe better understood from the followingdescription of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. I -1'9 Which it is Shown applied to a IOU-line P. A. X board. I

Fig. I shows the essential trunking arrangements of the board. I I

Figs. 2--5 when arranged in the manner indicated in Fig. 2 show circuits of two subscribers line equipments and of the local and special service link finder alle'tting' equipment and associated start relays. In Fig. 3 an explanatory inset is included to-simpl'ifythe understanding of the finding operations involved on origination of a local call. I I

Figs. 6, '7 and 3 when arranged side by side with Fig. 6 on the left show the circuit of a local finder/connector link, hereafter referred to as a local link. I I I I I Figs. 9 and 10 when arranged side by side show the circuit of a tie line service link.

Fig. 11 shows the circuit of a conference service equipment. Figs. l2;and- 13 when arranged side by side show the circuit of a fire alarm service link.

Figs. 14' and 15 when arranged side by side show the circuit of a watchmans service link.

Figs. 16-19 when arranged side by side inorder show the ci-rcuit of a code call service link.

-Considering first the general design of the 

